Conventionally, an automatic analyzer for analyzing a sample such as blood or urine includes a nozzle cleaning device for cleaning a dispensing nozzle in order to prevent carry-over which affects results of analysis as a result of carrying a previously-dispensed sample adhered to the dispensing nozzle over a sample subsequently dispensed. Such a nozzle cleaning device is disposed on a track where the dispensing nozzle moves, between a position where a sample is suctioned and a position where the sample is discharged, and is configured to supply the dispensing nozzle with a cleaning liquid. In a nozzle cleaning method using such a nozzle cleaning device, after suctioning and discharging the sample and completing dispensing, the dispensing nozzle is moved to the position of the nozzle cleaning device, the cleaning liquid is supplied to this dispensing nozzle, and the dispensing nozzle is cleaned.
In the nozzle after dispensing, a small amount of the sample remains, and if the dispensing nozzle is cleaned in a cleaning device in which a cleaning liquid is stored, the cleaning liquid is contaminated by the sample remaining in the dispensing nozzle. Thus, when a carry-over request level is high, a large amount of cleaning liquid is necessary for the cleaning process and the cleaning time is also long. In order to solve this, a method has been proposed in which a waste tank is installed adjacent to a cleaning tank and cleaning is performed after discarding a residual sample to the waste tank (see, for example, Patent Document 1).    Patent Document 1: Japanese Laid-Open Publication No. 2003-145077